Closer sagittal and meridional chart lines indicate more 'natural' out of focus areas.

Remember that MTF charts are good for comparing similar lenses, so comparing ones from the 14mm f2.8L and 300mm 2.8L won't tell you much at all, whilst comparing the EF14 2.8L with the EF14 2.8L II will show meaningful differences. Note that other manufacturers may have different ways of displaying such information that may or may not match up with the Canon figures.